SicHash -- Small Irregular Cuckoo Tables for Perfect Hashing

TL;DR

SicHash introduces a novel construction algorithm for perfect hash functions using irregular cuckoo tables, achieving improved space efficiency and fast query times compared to existing methods.

Contribution

The paper presents SicHash, a new direct construction algorithm for perfect hash functions utilizing irregular cuckoo hashing and small overloaded tables, enhancing space efficiency and construction speed.

Findings

Outperforms state-of-the-art in space usage

Reduces construction time significantly

Maintains very fast query performance

Abstract

A Perfect Hash Function (PHF) is a hash function that has no collisions on a given input set. PHFs can be used for space efficient storage of data in an array, or for determining a compact representative of each object in the set. In this paper, we present the PHF construction algorithm SicHash - Small Irregular Cuckoo Tables for Perfect Hashing. At its core, SicHash uses a known technique: It places objects in a cuckoo hash table and then stores the final hash function choice of each object in a retrieval data structure. We combine the idea with irregular cuckoo hashing, where each object has a different number of hash functions. Additionally, we use many small tables that we overload beyond their asymptotic maximum load factor. The most space efficient competitors often use brute force methods to determine the PHFs. SicHash provides a more direct construction algorithm that only rarely needs to recompute parts. Our implementation improves the state of the art in terms of space usage versus construction time for a wide range of configurations. At the same time, it provides very fast queries.